This invention relates to an image recording apparatus and, more particularly to an apparatus wherein one-component, conductive and magnetic developer (hereinafter simply called "toner") is imagewisely deposited on a recording material directly in response to electric image signals.
An image recording apparatus of this type has already been proposed, such as in U.S. patent application Ser. No. 22859, which will be briefly described in connection with FIG. 1. As is shown in this figure, the apparatus includes a stationary toner applying roller 1 which is in the form of a cylinder of non-magnetic material and which is dipped in the powder of conductive and magnetic toner T contained in a toner container 3. In the toner applying roller 1, there is a rotatable magnet 2 which is driven by an unshown driving mechanism. A recording electrode assembly 6 includes a number of electrode elements each made of a conductive and magnetic material. The electrode 6 is sandwiched by two opposing magnets 7 constituting magnetic field generating means.
When the magnet 2 rotates in the direction of arrow a, the conductive magnetic toner T moves from the container 3 along the surface of the applying roller 1 in the direction of arrow b and, after being subjected to a regulating function by a doctor blade 3', the toner is conveyed toward a recording material 4. The recording material 4 is shown as consisting of a cylindrical conductive base plate 4a and a dielectric layer 4b thereon, but is not limited to this type. Commercially available electrostatic recording paper is usable. Between the recording material 4 and the toner applying roller 1 in the illustrated arrangement, a voltage is applied by a power source 5, so that the toner T is attached on the recording material surface by an electrostatic force to form a thin layer thereof.
The thin coated toner layer T is conveyed, by the rotation of the recording material 4 in the direction of arrow, to the recording electrode 6 comprising a number of arrayed electrode elements which are electrically isolated from each other, whereat the toner particles are erected in the form of chains extending to reach to the tips of the recording electrode 6 under the action of magnetic force of the magnets 7. The contact of the toner with the electrode 6 discharges the charges, having been injected by the applying roller 1, through the chains of the toner particles and the recording electrode 6, so that there is now no attracting force between the recording material 4 and the toner T. At this instance, if an imagewise signal voltage is applied between the recording material 4 and the recording electrode 6 from a signal source 8, electric charges of opposite polarities appear, through the chain of toner particles, in the toner layer on the surface of the insulating layer 4b of the recording material 4 on one hand and in the back of the insulating layer 4b on the other hand, causing an attracting force to hold a part of the toner particles on the surface of the recording material 4.
The apparatus further includes a toner removing device 9 which removes by using air suction or the like those toner particles to which no attracting force has been applied, without disturbing the imagewise pattern of the toner particles held on the recording material 4, whereby a visualized image appears on the recording material 4. The thus visualized toner image is transferred to and fixed on a sheet of paper by a conventional corona discharging step, pressure-fixation step and the like. In a case where a commercially available electrostatic recording sheet is used as the recording material 4, the toner image may be directly fixed on the recording material.
Several disadvantages in the apparatus described in the foregoing has been found. The toner removing device 9 needs a bulky mechanism for producing air suction or the like. Further, a large space is required around the recording material. Moreover, those toner particles which can no longer be held on the recording material 4 are liable to be attracted by the force of magnetic field caused by the magnets 7 so that they are deposited on the magnets 7 and on the portion near the magnets. Therefore, during a long period operation, the deposited and accumulated toner particles will reach the recording material 4, soiling it or disturbing image formation.